1. Field of the Invention
The present invention relates to an optical apparatus for containing an optical member in a casing such as a lens-barrel into which nitrogen gas or the like is introduced, an exposure apparatus using the optical apparatus, and a gas introduction method.
2. Description of the Related Art
In conventional exposure apparatus, if oxygen exists in a space through which exposure light in an illumination optical system or in a projection optical system passes, when the exposure light is generated by a light source such as an ArF excimer laser, emission spectrum lines overlap on an area of oxygen absorption spectrum lines. Therefore, a phenomenon occurs where oxygen absorbs the exposure light, causing ozonization.
Therefore, there is a possibility that a tarnishing substance is deposited on the surface of the optical lens, adversely affecting the lens characteristics. Therefore, with conventional exposure apparatus, a part of the whole space around the optical path from the light source to a substrate to be processed is covered with a cover, and the inside of the cover is filled with a gas which is inert with respect to the exposure light, for example, nitrogen gas.
As a means for replacing gas in the optical path with nitrogen gas, for example, a structure as shown in FIG. 7 can be used. That is to say, in a structure where lenses 101 to 103 are clamped by spacing rings 104, 105 and surrounded by a lens-barrel 106, the nitrogen gas is introduced from a piping joint 107 which corresponds to an inflow device for the nitrogen gas. The nitrogen gas passes through an inflow passage 106a in the lens-barrel 106, and flows through a hole 104a opened in the spacing ring 104 to between the lenses 101 and 102 and the lenses 102 and 103. The space between the lenses 101 and 102, and the space between the lenses 102 and 103 are communicated with each other. The nitrogen gas flowing in between the lenses is discharged to the outside from a piping joint 108, passing through an outflow passage 106b having a similar structure.
However, with the above described conventional gas inflow device, the inflow passage 106a of the lens-barrel 106 coincides with the hole 104a of the spacing ring 104, and the nitrogen gas flowing from the hole 104a to between the lenses impinges concentratedly on one spot 102a of the lens 102 lying on an extension line of the hole 104a. Even with clean nitrogen gas, of purity of 99.999%, since dirt in the piping (outgassing of impurities generated by the piping itself) is contained therein, the above described one spot 102a is concentratedly contaminated, and the contamination rate at this spot becomes very high compared to at other places.
In view of the above situation, it is an object of the present invention to provide an optical apparatus which can reduce contamination on optical members such as lenses or the like due to the inflow gas, an exposure apparatus using the optical apparatus, and a gas introduction method.
To solve the above described problems, the optical apparatus of the present invention contains an optical member in a casing and comprises a gas introduction mechanism that reduces a flow rate of gas at the time of introducing a gas supplied at a predetermined flow rate from a gas supply device to inside the casing, to below the predetermined flow rate.
Moreover, in the gas introduction method of the present invention, when the gas supplied at a predetermined flow rate from the gas supply device is made to flow into the casing containing the optical member, the flow rate of the gas is decreased to below the predetermined flow rate.
According to the optical apparatus and the gas introduction method, when the gas supplied at a predetermined flow rate from the gas supply device is made to flow into the casing, the flow rate of the gas is decreased to below the predetermined flow rate. Therefore, when the gas reaches the surface of the optical member, the flow rate of the gas is decreased, and the gas is easily dispersed. As a result, adhesion of impurities contained in the gas onto the optical member can be suppressed, and the contamination rate of the optical member is retarded, enabling a significant improvement in the life span of the optical member.
The gas introduction mechanism is disposed between an inlet provided in the casing, and the surface of the optical member, and may comprise an impingement member or obstructer against which the gas introduced from the inlet is made to impinge. In this case, since the gas impinges against the impingement member to decrease the speed, adhesion of contained impurities onto the optical member can be suppressed.
The optical apparatus according to a second aspect of the present invention contains an optical member in a casing, and comprises a gas introduction mechanism that dispersingly introduce a gas from a plurality of places around the optical member, at the time of introducing the gas into the casing.
Moreover, with an other gas introduction method of the present invention, when a gas is made to flow into a casing containing an optical member, the gas is dispersed so as to flow from a plurality of places around the optical member.
According to the optical apparatus and the gas introduction method, since the gas is dispersed so as to flow from a plurality of places around the optical member, the place on the surface of the optical member against which the gas impinges is not concentrated at one spot, and the overall flow rate can be decreased compared to a case where the gas is concentratedly made to flow from one place. Therefore, impurities contained in the gas are unlikely to adhere to the optical member. Adhesion of impurities contained in the gas onto the optical member can thus be suppressed, thereby retarding the contamination rate, enabling a significant improvement in the life span of the optical member.
The gas introduction mechanism may comprise an annular member arranged in the casing so as to surround the optical member. In the annular member, there may be formed a circulation groove formed along the circumferential direction, in a face facing an inlet for the gas formed in the casing, and a plurality of through holes which are arranged circumferentially apart from each other so as to communicate with the circulation groove. In this case, the gas can be made to flow via the circulation groove from the plurality of through holes, enabling deceleration and dispersed inflow of the gas with a simple construction.
The through holes may be arranged at positions shifted from the gas inlet. In this case, it is possible to disperse and decelerate the gas introduced from the inlet by letting it impinge against the bottom of the circulation groove without flowing directly into a through hole.
The annular member may be a spacing annular member which is disposed between adjacent optical members and regulates the spacing of these optical members. In this case, the annular member can be formed by merely machining the spacing annular member, and can thus be realized at a low cost without increasing the number of members.
The gas introduction mechanism may have a filter that passes the introduced gas and adsorbs impurities in the gas. In this case, impurities intermixed with the gas in the piping can be removed to improve the gas purity, and further improve the life span of the optical member.
The exposure apparatus of the present invention is an exposure apparatus which guides exposure energy to a mask to thereby form a pattern on the mask onto the surface of a substrate. The apparatus comprises any one of the above-described optical apparatuses, and constitutes, using the optical members in the optical apparatus, at least one of an optical system that guides exposure energy to the mask, and an optical system that guides a pattern to the substrate.
According to the exposure apparatus, since at least one of an optical system that guides exposure energy to a mask, and an optical system that guides a pattern to a substrate, is constituted by the optical members in the above described optical apparatus, adhesion of impurities onto the optical members can be decreased, thereby improving the life span of the lens and reducing the maintenance costs, as well as preventing a decrease in exposure energy such as exposure light or the like, enabling efficient exposure.